The gym's gimmick would be that it function's similarly to the Battle Tower. You have to fight 7 trainers in a row with no heal, and then you get to fight the leader.
The gym rewards would be TM02: Dragon Claw and the Draconic Badge.
The battle theme is... the Pokémon Red and Blue Vs. Trainer theme. Coincidence? I think not. Well, regardless of whether or not iTunes is conspiring against me, I should put a link here, so, I guess I will. Here it is. (Note: the link takes you to an extended version.)

Quotes:
Pre-battle: You made it past the trainers. Quite impressive. However, it is time for your challenge to end.
Super effective: Dragon's can not be defeated that easily!
Last Pokémon: My dragon's will never fall to you!
Last weak: Is it... is it possible? Are dragon's not infallible?
I win: The sheer force of a dragon is unstoppable!
I lose: How could you defeat my army of dragons?
Rematch: You've returned? You will find that you will not win as easily this time.